Pyridine derivatives and process for the manufacture of same



Patented Nov. 12, 1946 PYRIDINE DERIVATIVES AND PROCESS FOR I THE MANUFACTURE OF SAME Max Hofier, Nutley, N. J assignor to Hofimann- La Roche, Inc., Nutley, N. J a corporation of New Jersey No Drawing. Original application September 2,

1941, Serial No. 409,298. Divided and this application May 11, 1945, Serial No. 593,317. In L Switzerland September 2, 1940 r l 2 Claims. (Cl. 260-:297)

The present invention concerns the synthesis of vitamin B6 (adermin) of the formula:

CHzOH I KOREA-OH I have found that the compound of 2-methyl-4- phenoxymethyl-cyano-6 -hydroxy pyridine-3- carboxylic acid (I) is an advantageous starting material for this synthesis. It is prepared by successively treating the condensation product, obtained from malonic acid dinitrile, phenoXyacetaldehyde-hydrate and acetoacetic ester, with an acid and a reducing agent, in accordance with Example 3 of any co-pending application S. N. 409,298, filed September 2, 1941, entitled EY- droxy-pyridine derivatives and process for the manufacture of same.

By treatment with phosphorus-pentachloride the 2-methyl- 4 -phenoxymethyl- 5-cyano-6-hydroxy-pyridine-3-carboxylic acid (I) is converted into Z-methyl- 4 -phenoxymethyl 5 cyano 6- chloro-pyridine-3-carboxylic acid chloride (II) and hydrazine caused to act thereon in the presence of free alkalis. The reaction can be illustrated by the following formulae:

It is surprising that it is possible to introduce the hydrazine radical in the side-chain in position 3 without the halogen reacting in the a-position, although it is known that a-halogen substituted pyridine derivatives can react easily with hydrazine (Journal of the Chemical Society of London, vol. 103, year 1913, page 1978 ,vol. 107,

. 2 1 ,7 year 1915, page 691; Monatshefte fur Chemie, vol. 36, year 1915, page 736). The desired reaction consequently only succeeds in presence of free alkalis. Curiously enough, the hydrazine'formed thereby. goes into the alkaline solution, from which it can be-precipitatedby neutralization of the alkali by means of free acids, ammonium salts or acid salts.

The 2-methyl-4-phenoxymethyb 5 .-cya no, 6,- chloro-pyridine-3rcarboxylic acid hydraz'ide (III) thus obtained i converted into the azide by nitrousacid or materials developing nitrousacid during the reaction, and the azide boiled with alcohols either after its isolation or in the reactionmixture to form 2-methyl-3-carbalkoxyamino -4-phenoxymethyl-5-cyano-6echloro pyridine. I

This compound can be converted inone step into 2-methyl- B-oarbalkoxyamino- 4 phenoxymethyl-5-arninomethyl-pyridine. Thehydrogenation ofthe cyanogroup to the aminomethyl group has often been-described in the literature- However, the working, is therebyeffected almost exclusively with palladium orplatinum as catalyst, in acid solution. On working in neutral solution 1 and with nickel catalysts, on the other hand, secondary amines are mostly obtained (Helvetica Chimica Acta, vol. 5, year 1922; page 937; vol. 6, year 1923, page 880; vol. 8, year 1925, page 848). Ithas now-been found that 2-methyl-3-carbalkoxyamino-4-phenoxymethy1- 5,-cyano-6-chlcropyridine, under suitableconditions, can also be reduced to the corresponding primary amine with nickel catalysts. Thereby, the chlorine atom in position 6 is simultaneously replaced by hydrogen. This course of the reaction could not be anticipated, for no case has become known so far where a chlorine atom adhering to a pyridine radical has been replaced by hydrogen by means of nickel as a catalyst. It Was rather to be expected that chlorine would be obstructive during the hydrogenation (Adkins Reactions of Hydrogen With Organic Compounds over Copper-Chromiumoxide and Nickel Catalysts, Wisconsin, year 1937, page 54; Schwoegler, Journal of the American Chemical Society, vol. 61, year 1939, page 3502).

The 2-methyl-3-carbalkoxyamino-4-phenoXymethyl-5-aminomethyl-pyridine is converted into 2-inethyl-3-carbalkoxyamino-4-phenoxy-methyl- (31120 CtHs Barlow-mania: mane-Non \NfCHB KNiCHa v 1 VI It has been found in the 2-methyl-3-carbalkoxy-amino-4-phenoxymethyl-5-hydroxymethylpyridine (IV) already at comparatively low temperatures not only the phenoxy radical can be saponified by treatment with hydrogen bromide, but also the urethane in one step. Thereby, Z-methyl-3-amino-4,5-dibromomethyl pyridine hydrobromide is obtained. By the action of water and nitrous acid or materials easily developing nitrous acid, it can readily be converted into adermin (VI, 2-methyl-3-hydroxy-4,5-dihydroxymethylpyridine) by heating. g 5

I have also found that the aforementioned] 2- methyl-4-phenoxymethyl-5-cyano-fi-chlormpyridine-3-carboiqrlic acid chloride (II) can be directly converted into the azide by treatment with sodium azide, and that 2-methyl- 3-carbalkoxyamino-4-phenoxymethyl-5-hydroxymethylpyridine (IV) may be saponified with diluted HClat elevated temperatures and then treated with nitrous acid or materials developing nitrous acid, for instance, silver nitrite.

It is to be noted that thevarious conversions of the difierent groups may occur in one step, for instance, the formation of the acid chloride in 3 position may be accomplished together with the conversion of the hydroxy group'in 6 position into halogen (chlorine) pyridine derivative. It can be done by acting upon the 2-methyl-4 phenoxymethyl-5-cyano-6-hydroxy pyridine-3-carboxylic acid with phosphorus pentachloride. Y 1 T Furthermore, the hydrogenation of the cyano group into the amino methyl groupmay take place concurrently with the substitution ofxthe halogen by hydrogen, or the splitting off of the phenoxy radical-by saponification='may occur si multaneously with the saponification of 'the urethane into the amine. Example I 20 parts by weight of 2-methyl-4-phenoxymethyl 5 cyano 6 hydroxypyridine 3 carboxylic acid are. heated with 35 parts; by weight of phosphorus-pentachloride and 50:Parts by weight of phosphorus-oxychloride or withgan other indifferent solvent under reflux, untiliallhas gone into solution andthe hydrogen-chloride evolution has ceased. The solventand the'phosphorus-oxychloride formed are distilled off in vacuo as completely as possible and the crystalline residue, representing theacid chloride of 2- 70 methyl 4 phenoxymethyl 5 cyano 6 ch1oropyridine-3-carboxylic acid,- taken up in about 200 parts by volume of warm benzene. A solution of '7 parts by'weight of hydrazine-hydrate in 100 parts by volume of a 10% solution onion I lyst and the of caustic soda is added dropwise to the benzene solution of the acid chloride while stirring,'

whereby the temperature is suitably kept below 30 C. Finally, another 50 parts by volume of a 10% solution of caustic soda are added and the mixture allowed to stand for 15 minutes. The brownish aqueous layer is removed from the henzene layer and acidified whereby the hydrazide separates as 'a brownish, crystallinef precipitate.

For the purpose of purification "the product can be triturated with dilute ammonia and sucked oil. Following this, it can be recrystallized from ethyl-acetate-petroleum ether. 2 methyl 4 phenoxymethyl 5 cyano 6-ch1oropyridine-3-carboxylic acid hydrazide is a colorless crystalline powder of melting point 114-115" C. Itis easily soluble in alcohol and ethyl acetate, diificultly soluble in the cold in benzene and ether. It is difiicultly soluble in water or petroleum ether. In dilute alkalis it is easily soluble and can be reprecipitated by addition of an acid, ammonium salts or acid salts.

10 parts by weight of 2-methyl-4-phenoxymethyl 5 cyano 6 chloropyridine 3 carboxylic acid hydrazide are dissolved in 50 parts by volume of absolute alcohol, a few drops of alcoholic hydrochloric acid and 5 parts by weight of amylnitrite added.

Crystalline precipitation of the azide quickly sets in, going into solution upon gentle heating with evolution of nitrogen. When the evolution of nitrogen has come to an end, the product is concentrated whereby 2-methyl-3 carbethoxyamino 4 phenoxymethyl 5 cyano 6 chloropyridine separates on cooling in the form of crystalline needles. For purification purposes the product is recrystallized from a little alcohol or from benzene. The melting point is at 167 C.

12 parts by weight of Z-methyl-B-carbethdxyamino 4 phenoxymethyl 5 cyano 6 chloropyridine are stirred up with 120 parts by weight of methanol,'1 2 parts by weight of-25% aqueous ammonia and 1.2 parts by weightof a nickel-catalyst (R-aney nickel) in a hydrogenation-autoclave at a gauge pressure of 20 atm. and simultaneously slowly heated to' 60 C. 3' mols of hydrogen are quickly taken up whereupon the hydrogenation is completely finished. The product is allowed to cool, separated from the cataentirely colorless filtrate dried in vacuo. The residue is taken up in 100 parts by volume of water, small quantities of undissolved material filtered oil, the filtrate rendered acid to v Congo paper with dilute hydrochloric acid and again evaporated to dryness in vacuo. The residue is recrystallized from ethanol. The resulting di-hydrochloride of 2-methyl-3-carbethoxyamino 4 phenoxymethyl 5 aminomethyl pyridine melts at 238 C. The yield amounts to of the theoretical.

10 parts by weight of 2-methy1-3-carbethoxyamino 4 phenoxymethyl 5 amino methylpyridine-hydrochloride are dissolved in parts by volume of 5% hydrochloric acid, the solution heated and a solution of 5 parts by weight of sodiumnitrite in water added dropwise at 90-95 C. After the evolution of nitrogen and oxides of nitrogen has ceased the product is allowed to cool and rendered alkaline with ammonia. The compound first separates as an oil and becomes'crystalline on standing. It is sucked-off and recrystallized from benzene. 2-methyl-3-carbethoxyamine 4 phenoxymethyl 5 hydroxymethylpyridine forms white prismatic needles of melt-;

ing point 127 C.

4 parts by weight of Z-methyI-B-carbethoxyamino 4 phenoxymethyl 5 hydroxymethylpyridine are heated with parts by volume of hydrobromic acid (about for 10 minutes at -70 C. until the CO2 development is terminated. The product is now evaporated in vacuo almost to dryness, allowed to crystallize overnight and taken up with alcohol in which the bromocompound is difiicultly soluble and is sucked off. By concentration of the mother liquor further quantities of the bromo-compound are obtained.

This is dissolved in parts by volume of wa ter and boiled for 20 minutes. Thereupon 10 parts by volume of 3-n hydrochloric acid are added and 1.5 parts by weight of freshly prepared silver nitrite quickly added while stirring at 90 C. After the cessation of evolution of nitrogen and oxides of nitrogen the product is filtered oiT from silver bromide and silver chloride and concentrated in vacuo. The residue crystallizes spontaneously, if need be upon rubbing with acetone, and proves to be vitamin Bra-hydrochloride (adermin) of melting point 206207 C.

Example [I 32 parts of the 2-methyl-4-phenoxymethyl-5- cyano 6 chloro pyridine 3 carboxylic acid chloride melting point -157 which has been prepared according to Example I are dissolved by 200 parts by volume dioxane while stirring. The solution is cooled to 5 C. and is dropped at that temperature into a solution of 10 parts of sodium azide in 50 parts of water. Stirring is continued for one hour during which the azide gradually precipitates. 100 parts of water are added to assist complete precipitation and the precipitate is suction filtered after some time, and is washed with water and then with a little cold alcohol. It is suspended in 300 parts of alcohol with stirring and is converted into the 2-methyl-4-phenoxymethyl-5-cyano-G-chlor-urethane and worked up into adermin, both as in Example I.

Example III 31.5 part of 2-methyl-4-phenoxymethyl-5- hydroxymethyl-pyridine-3urethane are heated in 500 parts of 2.5% hydrochloric acid to 1'70- C-. for 5 hours. The brown solution is decolorized with animal charcoal and is stirred up with 18 parts silver nitrite at YO-80 C'. The silver chloride is filtered off and the solution is concentrated in vacuo during which time adermin crystallizes from the solution.

This application is a division of my earlier application Serial Number 409,298, filed September 2, 1941.

What I claim is:

1. The compound 2 methyl 3 carbalkoxyamino 4 phenoxymethyl 5 hydroxy methyl-pyridine.

2. The compound 2 methyl 3 carbethoxyamino 4 phenoxymethyl 5 hydroxy methyl-pyridine, having a melting point of about 127 C. I

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